Extensible and contractible joist



May 7, 1963 A. T. JONES ET AL EXTENSIBLE AND CONTRACTIBLE JOIST 2 Sheets-Sheet 1 Filed May 20, 1959 May 7, 1963 A. T. JONES ETAL EXTENSIBLE AND CONTRACTIBLE JOIST 2 Sheets-Shee t 2 6017567 2 112; azyfleksrzzwzds p jeg Filed May 20, 1959 United States Patent 3,088,562 EXTENSIBLE AND CONTRACTIBLE JOIST Addis T. Jones, Chicago, and George S. Ellis, Lombard, IlL, assignors to Thomas Hoist Company, Chicago, Ill., a corporation of Illinois Filed May 20, 1959, Ser. No. 814,446 4 Claims. (Cl. 189-37) This invention relates to improvements in an adjustable joist which may be employed in supporting forms for concrete floors or ceilings.

In the laying of concrete floors or ceilings, it has heretofore been the practice to support the concrete forms for the floor or ceiling by erecting a plurality of Vertical columns more or less uniformly distributed beneath the area of the forms. In most instances the columns merely comprised timbers and the erection has usually been done as a custom construction operation and without the use of any prefabricated members. Such an operation has been both time-consuming and expensive.

:It has heretofore been proposed to use prefabricated extensible joist supported at their ends upon suitable columns or uprights, but the joists have been of such construction that the load, the laid concrete floor) was not efficiently distributed and, hence, such joists have been excessively heavy, making transportation and handling thereof a ditficult task. In addition, the joists are equipped with adjusting members which require the expenditure of time and labor before the forms are ready for pouring.

One of the objects of the present invention resides in the provision of a prefabricated, extensible joist which is so constructed that loads are efliciently distributed in its various extended positions which permits reduction of Weight of the joist for a predetermined load compared to those extensible joists heretofore proposed. This, in turn, permits easier transportation of the joists to and from the job, and, of extreme importance, permits easy handling of the joists on the job.

Another important object of the present invention resides in the provision of an extensible joist which when positioned in operative position requires no adjustments, or the use of screws or clamps.

A further important feature of the invention resides in a joist, the upper portion of which can be readily leveled and which carries a wooden member that serves as a nailing foundation for the plywood concrete forms which are supported thereon.

Other objects and advantages of the present invention will be apparent from the accompanying drawings and following detailed description.

In the drawings:

FIG. 1 is a side elevational viewillustrating the extensible joist embodying the features of the present invention, the joist being supported on vertical columns.

FIG. 2 is an enlarged elevational view of the outer joist member.

FIG. 3 is a top plan view of the outer joist member illustrated in FIG. 2.

FIG. 4 is a bottom plan view of the outer joist member shown in FIG. 2.

FIG. 5 is an enlarged elevational view of the inner joist member.

FIG. 6 is an enlarged cross-sectional view taken on 'line 66 of FIG. 1.

FIG. 7 is a fragmentary detailed view of abutting ends of end-adjacent joists.

FIG. 8 is an enlarged fragmentary detailed sectional view of a modified assembly wherein two joists are aligned end-to-end.

FIG. 9 is a sectional view taken on line 9--9 of FIG. 1.

Referring in detail to the drawings, 1, 1 indicate a pair of spaced vertical supports or columns which are adapted to carry an extensible joist 2 embodying the features of the present invention. A transverse beam 3 may be positoned upon each of the columns and may extend at rightangles to the columns. Thus, throughout the length of the structure a pair of spaced columns 1 may support one or more extensible joists 2.

'Each joist 2 comprises an outer joist member 4 and an inner joist member 5, the joist members being telescopically related to each other to span the distance determined by the spacing of the pair of columns 1. Thus, an extensible joist 2 may be employed with a range of spacings of columns 1 which may determine various widths of the concrete floor or ceiling to be laid.

Each outer joist member 4 comprises a lattice or skeleton frame construction which is substantially trapezoidal in cross-section, as shown best in FIG. 6, the top portion being of greater width than the bottom portion. The top portion of the member 4 comprises a pair of spaced anglesectioned rails 6 which are joined together and spaced by transverse spacer bars 7 which may be secured to the rails by welding 8 or the like, the bars being spaced from each other along the length of the rails.

The lower portion of the outer joist member 4 comprises a channel 9 which is offset lengthwise with respect to the rails 6. A plurality of struts or braces 10 are joined at their ends to each of the rails 6 and the channel 9 thereby forming a rigid, latticed frame. One upper corner portion of the frame, thus formed, comprises a box construction which functions as an abutment 11 whereby said frame may be seated at one end upon one beam 3.

A bearing plates 12 is secured to flanges of the channel 9 to form a box beam construction. At the diagonally opposite corner of the outer joist from the member 11, overhanging flanges 13 are carried by the opposite flanges of the channel 9, the edges of the flanges 13 being spaced from each other to provide a slot 14 (FIG. 3).

The inner joist member 5 is generally of triangular cross-section and comprises at its top, an elongated wooden block or board 16, which comprises the base of the inverted triangular structure. A pair of panels 17, constructed of metal, are secured at corresponding edges to opposite sides of the board 16. The panels are inclined toward each other and adjacent the apex of the triangular structure the edges of the panel are secured rigidly to a metallic web 18, said web being substantially coextensive in length with the panels 17. At the opposite edge of the web 18 a cross-flange 19 is integrally joined to the web, the web and cross-flange forming an inverted T-iron. A box structure 20, similar to the box structure 11, is carried at an upper corner of the inner joist member and functions as an abutment for seating upon the opposite beam 3.

In elevation, the inner joist member 5 is of substantially skewed parallelogram shape generally similar to the elevation of the outer joist member.

When the outer and inner joist members are assembled, an end portion of the inner member is telescopically positioned within the outer member with the T- flange 19 of the inner member threaded through the space 14 defined by the edges of the flanges 13 and the plate 12. In use, the T-flange 19* will be threaded through space 14 and at greatest extensibility, the end portion of the T flange 19 diagonally opposite the box structure 20 will be disposed adjacent the flanges 13. At minimum extensibility, an intermediate portion of the T flange 19' will be confined by the edges of the overhanging flanges 13 and the top of the bearing plate 12 and the end of the T-flange will be in pressure contact with the bearing plate. In other words, the flange 19 Will exert an upwardly directed force upon the edges of the overhanging I flanges 13, and the outer end of the flange 19' will exert a downwardly directed force upon the top of bearing plate 12. Thus, by sliding the structures 4 and 5 toward or away from each other a wide range of column spacings may be used.

As an important feature of the present invention, the upper face of the board 16 will always be spaced from the lower surfaces of the rails 6 and cross-members 7 of the outer joist member. Thus, the load of the concrete floor or ceiling carried upon the upper portion of each joist 2 will be borne by the T-flange 19 and the flanges 13 and will not be borne by contact of the upper portion of the inner joist member and the inner faces of the rails and cross-members of the outer joist member.

It has been found that with this construction the joist 2 may be extended and contracted with a minimum of labor; the upper surfaces of the joist members may be maintained substantially parallel to each other in various degrees of extensibility; and throughout a Wide range of spacings of columns 1, the load borne by the joist 2 will be relatively uniformly distributed. Thus, for predetermined loads and predetermined maximum spans, the joist members may be constructed of lighter weight than has heretofore been possible. This, of course, facilitates maneuverability and handling on the job and transportation to and from the job as Well as cost of joist construction.

Also, in view of the fact that the inner joist member will always span at least fifty percent of the distance between columns 1, the board 16 provides a convenient nailing support for the concrete forms supported upon the upper surface of the joist.

The floor or ceiling forms (not shown) Which usually comprise plywood, may be laid directly upon the upper surfaces of the joist. If desired, however, stringers may be supported directly upon the joists which, in turn, may be used to support the plywood forms. Although the joist 2, comprising the joist members 4 and 5, is shown as having its upper surfaces flat, the joist members may, if desired, be constructed with a slight degree of convexity upwardly, that is, they may be cambered so as to assume a relatively flat position when the load of the floor or ceiling is applied. The degree of such convexity will be extremely small and will not interfere with the free telescopic movement of the joist members relative to each other.

As an example of an extensible joist embodying the features of the present invention, a joist having a maximum span of about 20 feet, had a minimum span of about 12 feet 6 inches; the space between the upper surface of the board 16 from the lower surfaces of the rails 6 and cross-members 7 Was about of an inch. Joists having these general dimensions were found to operate exceedingly well and were easily handled and transported. Of course, the dimensions set forth above are for example only and are not intended as a limitation.

Referring particularly to FIG. 7, a fragmentary detailed view is shown of the juncture of two end-abutting joists embodying the features of the present invention. As has been hereinbefore described, the abutment 11 at the outer end of the outer joist member 4 and the abutment 20 at the outer end of the inner joist member 4 are of box structure, that is, they are of hollow construction.

In employing the joists comprising the present invention it frequently happens that the area of concrete supported by the joists is such that joists 2 are erected end-toend. In this case a single row of standards or shores may support the abutting ends of the joists. Conveniently, the abutments 11 and 20 are so constructed as to permit the telescopic engagement of the abutment 11 of joist member 4 within abutment 20 of joist member 5. Thus, the joists 2 may be erected end-to-end and virtually form an elongated multiple joist. By virtue of the engagement of the inner and outer joist members to form the extensible or contractible joist 2 and the fact that said joist has the load. uniformly distributed thereon, the abutments 11 and 20, when the joists are in end-abutting relationship will be brought to and remain in substantial axial alignment which facilitates the telescopic engagement of the abutments 11 and 20.

It sometimes becomes desirable, to erect the joists 2 in longitudinal alignment whereby the adjacent ends of an inner joist member of one joist and the outer joist member of the aligned joist are spaced from each other. For instance, where a drop head 20 FIG. 8, is employed as a cap or load-distributing agent for a row of central columns 21.

In a construction of the type illustrated in FIG. 8, the abutment 20* carried by joist member 5 .is supported by a shore 1a and the. abutment 11 carried by joist member 4 of an end-adjacent joist 2 is supported by a spaced shore 1b, the shoreslw and 1b being positioned on opposite sides of the column 21 and on opposite sides of the drop head 20'. By virtue of the box structure of the adjacent abutments 11 and 20, a beam 22, such, for instance, as a 4" by 4" wooden beam, may be inserted in the aligned abutments 11 and 20 and thus bridge the shores, furnishing support for the drop head form 23. In this case, plywood forms 24 and 25 may be carried on cross-beams 26 which, in turn, are supported on the joists 2.

Even where a drop head, such as, drop head 20- is not to be erected, it may be desirable to independently support the adjacent ends of the end-aligned joists on separate spaced shores. In this case a beam, similar to beam 22, may function as a bridging means between the adjacent ends of the joists. This may be the case Where the ceilings are high and the shores 1a and 1b are so long as to make buckling a possibility.

Here again, by virtue of the unique engagement of the joist members 4 and 5, hereinbefore described, the axes of the abutments 11 and 20 will be in substantial alignment due to the negligible deflection of the end-aligned joists. This, of course, facilitates the installation of the bridging beams 22.

We claim as our invention:

1. An extensible and contractible joist comprising an outer joist member and an inner joist member disposed in telescopic relationship to each other, said outer joist member comprising a top frame, a bottom frame and side frame members defining a hollow frame construction, the inner joist member having a top member, side members and terminating at its bottom in a lateral projection, said inner joist member being of a height less than the spacing between the top and bottom frames of said outer joist member, but the top frame of the outer joist member and the extended portion of the top member of the inner joist member defining a generally continuous unobstructed horizontal load bearing surface, overhanging projection means carried by the bottom frame of the outer joist member at an end thereof, said overhanging projection means overhanging said lateral projection of the. inner joist member permitting slidable movement of said inner joist member relative to said outer joist member but restricting upward movement of said inner joist member within said outer joist member to space the top member of the inner joist member a short distance. below the top frame of the outer joist member, and a plate carried by said bottom frame of the outer joist member adjacent said overhanging projection means restricting downward movement of said inner joist member Within said outer joist member to maintain the top member of the inner joist member in substantially plane-parallel spaced relationship to the top frame of the outer joist member, thereby to cause said inner joist member in use to be loaded in tension at the juncture of said inner joist member with the end of said outer joist member and to prevent the application of crushing force from the outer joist member to the top frame member of the inner joist member.

2. A horizontal extensible and contractible joist comprising an outer joist member and an inner joist member disposed in telescopic relationship to each other, said outer joist member comprising a top frame, a bottom frame and side members defining a hollow frame construction, the inner joist member having a top member and side members defining a panel construction substantially infinitely adjustable relative to the outer joist member for load-bearing purposes, said inner joist member being of a height less than the spacing between the top and bottom frames of said outer joist member but the top frame of said outer joist member and the extending portions of the top member of said inner joist member defining a generally continuous unobstructed horizontal load bearing surface, said inner joist member terminating at its bottom in an inverted T-flange, and a set of laterally spaced projections carried by the bottom frame of the outer joist member at one end thereof, the set of projections comprising a pair of flanges extending above said bottom frame and turned inwardly toward each other over the horizontally extending portions of said T-flange of the inner joist member and accommodating slidable movement of said joist members relative to each other, the bottom frame of the outer joist member engaging the bottom of said T-flange and preventing downward movement of the end of the inner joist member telescoped therein, said inwardly turned flanges of the outer joist member engaging over the horizontally extending portions of said T-flange and restricting upward movement of the engaged portion of the inner joist member within said outer joist member to space the top member of the inner joist member a short distance below the top frame of the outer joist member, thereby to interconnect said joist members by virtue solely of said T-flange, the bottom frame of the outer joist member and said projections, to cause said inner joist member in use to be loaded in tension at the juncture of said inner joist member with said one end of the outer joist member and to prevent application of localized crushing force from said outer joist member to the top member of said inner joist member.

3. A horizontal extensible and contractible joist comprising an outer joist member and an inner joist member disposed in telescopic relationship to each other, said outer joist member comprising a top frame, a bottom frame and latticed side frame members defining a hollow open frame construction having longitudinally spaced panel points along the top and bottom frames thereof, the inner joist member having a top member and side members defining a panel construction substantially infinitely adjustable relative to the outer joist member for load-bearing purposes, said inner joist member being of aheight less than the spacing between the top and bottom frames of said outer joist member but the top frame of said outer joist member and the extending portions of the top member of said inner joist member defining a generally continuous unobstructed horizontal load bearing surface, said inner joist member terminating at its bottom in an inverted T-fiange, and a set of laterally spaced projections carried by the bottom frame of the outer joist member at a panel point adjacent one end thereof, the inner joist member being telescoped into said one end of said outer joist member and extending at the T-fiange thereof over the panel point at which said projections are located and a second inwardly spaced panel point of the bottom frame of said outer joist member, said T-flange bearing downwardly on the bottom frame of said outer joist member at said second panel point, the set of projections comprising a pair of flanges extending above the bottom frame of said outer joist member and turned inwardly toward each other over the top of the horizontally extending portions of said T-flange of the inner joist member, said inwardly turned flanges of the outer joist member permitting slidable movement of said joist members relative to each other but restricting upward movement of the inner joist member within said outer joist member to space the top member of the inner joist member from the top frame of the outer joist member, thereby to interconnect said joist members solely at said first and second panel points by virtue solely of said T- flange, the bottom frame of the outer joist member and said projections, to cause said inner joist member in use to be loaded in tension at the juncture of said inner joist member with the one end of the outer joist member and to prevent application of localized crushing force from said outer joist member to the top member of said inner joist member.

4. A horizontal extensible and contractible joist comprising an outer relatively elongated joist member of hollow latticed construction defining a plurality of longitudinally spaced panel points, an inner relatively elongated joist member of panel construction telescoped into said outer joist member and substantially infinitely adjustable rel-ative thereto, both of said joist members having top and bottom portions, said top portions being spaced apart a short distance but nevertheless defining a generally continuous unobstructed horizontal load bearing surface, the bottom portion of the inner joist member at the end portion thereof telescoped into said outer joist member engaging the bottom portion of the outer joist member over at least two of the panel points on said bottom portion, a longitudinally extending structural member earned by the bottom portion of the inner joist member along the length thereof and having upwardly exposed lateral surfaces, and projection means carried at a panel point adjacent the end of the bottom portion of the outer joist member, said projection means engaging over the lateral surfaces of said structural member and accommodating relative slidable movement of the joist members but restricting upward movement of the inner joist member with respect to the outer joist member to maintain the top portion of the inner joist member in spaced relation to the top portion of the outer joist member, thereby to interconnect said joist members solely by said structural member, the bottom portion of said outer joist member and said projection means, to cause said inner joist member in use to be loaded in tension at the juncture of said inner joist member with the end of the outer joist member and to prevent application of localized crushing force from said outer joist member to the top portion of the inner joist member.

References Cited in the file of this patent UNITED STATES PATENTS 1,848,476 Hall Mar. 8, 1932 2,726,743 Short et a1 Dec. 13, 1955 2,974,762 Hunnebeck Mar. 14, 1961 FOREIGN PATENTS 406,645 Great Britain Feb. 15, 1934 330,032 Switzerland July 15, 1958 967,267 France Mar. 22. 1950 

1. AN EXTENSIBLE AND CONTRACTIBLE JOIST COMPRISING AN OUTER JOIST MEMBER AND AN INNER JOIST MEMBER DISPOSED IN TELESCOPIC RELATIONSHIP TO EACH OTHER, SAID OUTER JOIST MEMBER COMPRISING A TOP FRAME, A BOTTOM FRAME AND SIDE FRAME MEMBERS DEFINING A HOLLOW FRAME CONSTRUCTION, THE INNER JOIST MEMBER HAVING A TOP MEMBER, SIDE MEMBERS AND TERMINATING AT ITS BOTTOM IN A LATERAL PROJECTION SAID INNER JOIST MEMBER BEING OF A HEIGHT LESS THAN THE SPACING BETWEEN THE TOP AND BOTTOM FRAMES OF SAID OUTER JOIST MEMBER, BUT THE TOP FRAME OF THE OUTER JOIST MEMBER AND THE EXTENDED PORTION OF THE TOP MEMBER OF THE INNER JOIST MEMBER DEFINING A GENERALLY CONTINUOUS UNOBSTRUCTED HORIZONTAL LOAD BEARING SURFACE, OVERHANGING PROJECTION MEANS CARRIED BY THE BOTTOM FRAME OF THE OUTER JOIST MEMBER AT AN END THEREOF, SAID OVERHANGING PROJECTION MEANS OVERHANGING SAID LATERAL PROJECTION OF THE INNER JOIST MEMBER PERMITTING SLIDABLE MOVEMENT OF SAID INNER JOIST MEMBER RELATIVE TO SAID OUTER JOIST MEMBER BUT RESTRICTING UPWARD MOVEMENT OF SAID INNER JOIST MEMBER WITHIN SAID OUTER JOIST MEMBER TO SPACE THE TOP MEMBER OF THE INNER JOIST MEMBER A SHORT DISTANCE BELOW THE TOP FRAME OF THE OUTER JOIST MEMBER, AND A PLATE CARRIED BY SAID BOTTOM FRAME OF THE OUTER JOIST MEMBER ADJACENT SAID OVERHANGING PROJECTION MEANS RESTRICTING DOWNWARD MOVEMENT OF SAID INNER JOIST MEMBER WITHIN SAID OUTER JOIST MEMBER TO MAINTAIN THE TOP MEMBER OF THE INNER JOIST MEMBER IN SUBSTANTIALLY PLANE-PARALLEL SPACED RELATIONSHIP TO THE TOP FRAME OF THE OUTER JOIST MEMBER, THEREBY TO CAUSE SAID INNER JOIST MEMBER IN USE TO BE LOADED IN TENSION AT THE JUNCTURE OF SAID INNER JOIST MEMBER WITH THE END OF SAID OUTER JOIST MEMBER AND TO PREVENT THE APPLICATION OF CRUSHING FORCE FROM THE OUTER JOIST MEMBER TO THE TOP FRAME MEMBER OF THE INNER JOIST MEMBER. 